Chip packaging is often intensely involved with heat removal. Thermal expansion-mismatch challenges exist between the die, the underfill material, and the substrate to which the die is mounted, and to connecting structures such as the motherboard. The thermal mismatch often is exhibited at the joint of a solder bump and its bond pad.
One challenge with chip packaging technology is premature solder joint failure due to thermal stress. Future packaging technology especially in the chipset application, will drive finer pitch as package size shrinks. With miniaturization of pitch, smaller ball size poses an increasing challenge to solder joint performance.
Two types of failure have been observed in solder bumps. One type is fatigue due to thermal stressing at the solder joint. Another type of failure results from mishandling the packages during processing, assembly, and transportation. These failures are primarily due to higher stress levels at the solder bump-contact pad interface. The solder joint has been observed to crack at the edges, and due to poor adhesion of the bumps to the pad, the solder has been observed to break away from the pad.